Generic Circumscription in the Family Ectocarpaceae (Phaeophyceae)

Abstract

The family Ectocarpaceae currently contains the simplest, and probably also the most primitive, members of the Phaeophyceae. The thallus form of every species is a heterotrichous filament with little or no structural modification. Some species may possess quite extensive cortication of axial filaments by adventitious rhizoids but advanced pseudoparenchyma is never formed. Periclinal cell divisions within filaments have also been reported, particularly in the course of sporangium development, but true parenchyma is unknown. Growth of the erect system of filaments is diffuse, for although intercalary sites of relatively active cell division may sometimes be observed, these lack the permanence of position and sustained activity of true intercalary meristems. The growth of the horizontal branch system is probably mainly apical, but is also too diffuse to be considered meristematic. Sporangia and gametangia are formed from vegetative cells and occur either as intercalary structures within filaments or as modified branch apices. Sexual fusion of gametes may be isogamous or anisogamous.